This invention is in the field of foods for “companion animals,” such as dogs or cats. All references herein to food of any sort are intended to refer only to food that is manufactured and marketed for companion animals, such as dogs or cats. Although testing to date has focused on dogs, this invention can also be adapted for use with cats, pot-bellied pigs, ferrets, and similar classes of companion animals which generally are carnivorous or omnivorous.
If desired, the invention disclosed herein also can be tested to evaluated its suitability for use with still other classes of animals, including rodents (hamsters, guinea pigs, rabbits, etc.), birds, and reptiles, as well as for horses and any type of livestock. However, since dogs and cats show higher levels of sensitivity to taste and aroma than rodents, livestock, and most other classes of animals, and since dogs and cats form the largest categories (by far) of animals which receive flavor-enhanced animal foods, this text uses the term “pets”, for convenience, to refer to any and all animals that are likely to receive the types of flavor-enhanced foods that are described herein. For convenience, a food product which is manufactured and marketed for animals, and which is likely to benefit from a flavor and/or palatability enhancer as disclosed herein, is referred to herein simply as a pet food, animal food, etc.
Pet foods are divided into several categories, because the packaging needs of the different categories differ substantially. At one end of the spectrum, high-moisture foods typically contain relatively high quantities of meat, and usually need to be packaged in cans, to prevent rapid degradation by bacteria, fungus, and other microbes.
In the middle of the moisture spectrum, pet foods with intermediate levels of moisture are often called soft dry, soft moist, semi-dry, or other comparable terms. These are not precise terms; instead, they indicate general categories that affect the type of handling and packaging that must be used for different formulations. In general, “soft dry” foods (usually with moisture content of about 12% up to about 20%) can be stored in bags made of heavy paper (or in cardboard boxes, canisters, etc.), without requiring a water-impermeable foil or plastic lining. “Soft-moist” foods (about 20% to about 40% moisture) can often be stored in a bag or box rather than a can, but the bag or box usually will require an impermeable foil or plastic lining.
At the low end of the moisture scale, “dry foods” (also called low-moisture foods) usually contain less than about 12 to 15% moisture, and usually produce a crunching sound when chewed by a pet. The particulate chunks in most dry foods are prepared from plant-derived materials, which provide protein, carbohydrates, fiber, and other bulk material.
Most dry pet foods, and many types of soft dry, soft moist, and semi-dry pet foods, are formed by pelleting or extrusion processes, which can provide high volumes at low cost. The term “kibbles” is used herein (and generally within the pet food industry) to refer to particulate chunks formed by either a pelleting or extrusion process. Typically, kibbles tend to have spherical, cylindrical, oval, or similar shapes, and they typically have a largest dimension of less than about 2 cm (about 1 inch).
By contrast, larger pet food items that are designed to be fed to a pet, one at a time, by the owner, to help promote or sustain a bonding process between a pet and its owner, are usually called biscuits or treats, within the pet food industry. Such items are referred to herein as “biscuits”. They usually are formed by a process that involves molding, followed by baking or other cooking process to harden the dough, paste, or similar material that was molded. Pet food biscuits often contain (or are coated with) palatability-enhancing agents, in a manner comparable to the use of palatability-enhancing agents with kibbles; accordingly, although the discussion below refers mainly to kibbles, it should be understood that this invention is equally applicable to pet food biscuits and treats.
Similarly, although the examples and narrative below refer mainly to dry and semi-dry kibbles (since those types of foods pose the greatest challenge, with respect to making them appealing to dogs and cats), it should be understood that the palatability-enhancing agents disclosed herein can also be used with semi-moist or even canned pet foods.
Since dogs and cats generally prefer moist and meaty foods over chunks of dried plant material, kibbles (especially in low-moisture pet foods) usually must be coated by a powdered or liquid preparation that will provide the kibbles with a meaty, fishy, or other aroma and taste which appeals to dogs or cats. These types of coatings are often referred to as “palatability” enhancers, where “palatability” is an overall term that refers to the willingness of pets and test animals to eat a certain food and be satisfied by that food. Palatability includes all of the organoleptic (sensory) factors that affect the way a food is perceived by an animal; these factors includes aroma, taste, aftertaste, texture, “mouth feel”, etc. Because “palatability” is an awkward polysyllabic word, the term “flavor-enhancer” is often used in its place, for convenience. Any references herein to “flavor-enhancing” or similar terms are used for convenience, and refer more precisely to “palatability-enhancing” traits. As is common in the industry, the term “flavor-palatability enhancing” is also used herein, since it can be referred to by the acronym “FPE”.
As used herein, terms such as “flavor-enhancing” or “palatability-enhancing” also encompass traits that make a pet food appealing not just to pets, but to pet owners as well. Pet owners will not buy a pet food that has (for example) an aroma that humans consider offensive and disgusting, or which has such a high level of greasiness that it clings to an animal's mouth area and fur and poses problems of staining on carpets, furniture, etc.
Prior Art Flavor-Enhancers; Two-Bowl Tests
Extensive efforts have been made to develop various chemical additives and mixtures that will enhance the flavor (palatability) of non-canned foods for dogs and cats. Examples of such efforts are described in various texts, such as Small Animal Clinical Nutrition, 3rd edition (L. D. Lewis, M. L. Morris, and M. S. Hand, authors; published by Mark Morris Associates, Topeka, Kans., 1987), and in numerous U.S. patents, including U.S. Pat. Nos. 3,857,968 (Haas and Lugay 1974, covering a mixture of emulsified fat and protein, treated with lipase and protease enzymes and used as a spray coating); U.S. Pat. No. 3,930,031 (Kealy 1975, covering mixtures of phosphoric and citric acids); U.S. Pat. No. 4,089,978 (Lugay et al 1978, covering a mixture of sugar, animal blood, yeast, and fat, treated with lipase and protease enzymes); U.S. Pat. No. 4,160,038 (Groben et al 1979, covering mixtures of meat and vegetable proteins, fermented by bacteria that produce lactic acid); U.S. Pat. No. 4,191,781 (Schara et al, covering additives containing ammoniated glycyrrhizin); U.S. Pat. No. 4,211,797 (Cante et al 1980, on coatings made from lipolyzed beef); U.S. Pat. No. 4,267,195 (Boudreau et al 1981, covering various amino acids mixed with nucleoside phosphates); U.S. Pat. No. 4,282,254 (Franzen et al 1981, covering various amino acids); U.S. Pat. Nos. 4,391,829 and 4,393,085 (both by Spradlin et al 1983, covering digestion of grain products and meat products using both an amylase enzyme and a protease enzyme); and U.S. Pat. No. 4,784,860 (Christensen 1988, covering the treatment of vegetable protein with bacterial SPS-ase enzymes to convert polysaccharides into texture-enhancing components).
The effects of any proposed additive in an animal food can be measured by a test that is commonly called the “two-bowl consumption test”, or simply “two-bowl test”. In this type of test, a hungry animal is given a choice of two bowls, having two food preparations that are identical in their basic composition but which have different additives. The animal is allowed to select and eat the food it prefers, from the two choices.
For example, in tests using dogs, a dog in a pen or cage can be given equal amounts of food in Bowl A and Bowl B. Bowl A will contain a “control” food with a standard coating agent, and Bowl B will contain the same type of food, with the same standard coating agent, and with an added compound that is being tested as a palatability enhancer.
Depending on what types of comparisons are desired, the control food in Bowl A might be a standard extruded dry (“kibbles”) base, which has been lightly coated with nothing but a standard coating agent that is used in nearly any dry food, such as poultry oil or beef tallow. However, testing a candidate FPE agent against a low-cost “basal” preparation is not a rigorous and convincing test, and will not indicate whether a candidate agent will be good enough to compete in the highly competitive market for dog and cat foods. Therefore, the control food in Bowl A preferably should be coated not just with a standard spray of poultry oil or beef tallow, but also with a known product that has fairly good FPE properties, such as a “liver digest” (a liquid which typically is formed by fermenting chicken, pork, or beef livers with hydrolytic bacteria). Testing a candidate FPE agent against a known FPE product such as a liver digest offers a more rigorous and revealing test of how good the candidate FPE agent really is.
The amount of food in Bowl A and Bowl B is weighed before the two bowls are offered to the dog. During the test, steps are taken to ensure that the dog does not finish the food in one bowl and then eat food from the other bowl because it is still hungry; this can be done by limiting the time of access to the bowls, and/or by providing enough food in either bowl to fully satisfy the dog.
After the dog has finished eating (or after the test period has ended), the two bowls are weighed again, to determine how much food was eaten from each bowl. The larger quantity is divided by the smaller quantity, to provide a ratio that is greater than 1.0. If more food was eaten from Bowl B (with the candidate flavor enhancer), the ratio is recorded as a positive value, to indicate that the palatability enhancer had a positive effect. If more food was eaten from Bowl A (the control food, without the candidate flavor enhancer), the ratio is recorded as a negative value, to indicate that the candidate flavor enhancer did not perform as well as the control food it was being tested against.
However, a negative ratio doesn't necessarily mean the candidate compound failed the test; for example, if an inexpensive flavoring agent (or a more expensive agent, at a low concentration) can come reasonably close to matching a very expensive premium flavor enhancer, the inexpensive or low-concentration agent might be regarded as being competitive and useful in pet foods. It also should be recognized that ratios of less than about 1.5 or 2 often do not indicate major differences in preference, and many food scientists commonly regard ratios less than about 1.5 or 2.0 as indicating that two preparations are roughly comparable.
By contrast, a good flavor enhancer will often generate consumption ratios that are higher than about 4 or 5, if compared to a basal food that has been coated with nothing more than poultry oil or beef tallow. Indeed, consumption ratios that approach infinity are not uncommon. In a two-bowl test, nearly all dogs or cats will sniff both bowls. If one bowl smells substantially better than the other, the animals will eat only from the bowl with the preferred fragrance, and consumption from the other bowl may be a flat zero.
When viewed by those standards, a low preference ratio (about 2 or less) indicates that two competing additives are nearly comparable. Test animals ate substantial quantities of both foods, and did not take just one or two bites from the less-preferred bowls and then eat the entire remainder of their food from the preferred bowls.
Two-bowl consumption tests were done on the compounds described below, using statistically significant numbers of animals (at least 10 animals in each test group), for at least two days in each test. For each test group, the total weight of the food eaten from the A and B bowls was added up, for all dogs in that test group. A ratio was then determined, based on those weight totals. The tests were done by independent testers, at kennels located away from the food manufacturing site, using number-coded foods so that the people who worked with the animals did not know which compound was present in any coded food preparation.
As described below, these tests evaluated a new class of flavor (palatability) enhancers in non-canned animal foods. The results indicated good results, when tested in dogs; the new class of flavor enhancers performed well, even when compared to premium flavor enhancers. Although tests have not yet been carried out in other types of pets, it is believed that these flavor enhancers are likely to perform well in many types of carnivorous animals (including cats, ferrets, pot-bellied pigs, etc.), and possibly in various types of herbivores as well.
Oils, Fats, and Triglycerides
Since the methods of this invention relate to chemical treatment of vegetable oils and/or animal fats, some background information on the chemistry of vegetable oils and animal fats should be taken into account.
Briefly, vegetable oils as well as animal fats both contain large quantities of molecules called “triglycerides”. These molecules are also called “triacylglycerides”, mainly by molecular biologists; the term “triglyceride” is no longer favored in molecular biology, but it is still the common term in the food industry.
Triglyceride molecules are formed when three fatty acid molecules react with a compound called glycerol. Glycerol is a short “poly-alcohol” molecule, with only three carbon atoms, each carbon atom having a single hydroxy group bonded to it, as follows:

The types of fatty acids which are of interest herein (and in nature) are hydrocarbon molecules which have a carboxylic acid group at one end. A carboxylic acid group, R—COOH, readily releases its hydrogen proton, thereby forming the resulting anion, R—COO−. When a carboxylic acid group on a fatty acid molecule reacts with one of the hydroxy groups on glycerol, the hydroxy group (from the glycerol) and the hydrogen proton (from the carboxylic acid group of the fatty acid) combine to form a water molecule, which is released. The type of covalent bond that is formed between the glycerol molecule and the fatty acid is generically called an ester bond; in an ester bond, a single carbon atom is double-bonded to a first oxygen atom which is not in the main chain, and single-bonded to a second carbon atom which is part of the main chain. Three ester bonds are present in the triglyceride molecule shown below.
Ester bonds are so frequent and so important in biochemistry that they are subdivided into various subcategories having their own names; accordingly, the type of ester bond that is formed between a glycerol molecule and a fatty acid molecule, in the type of biochemical reaction that creates fat, is called a glyceride bond.
If glycerol bonds to a single fatty acid molecule, the resulting molecule is called a mono-glyceride. If a single molecule of glycerol bonds with two fatty acid molecules, the result is called a di-glyceride. If all three of the hydroxy groups in a molecule of glycerol react with fatty acid molecules, the result is a tri-glyceride.
A typical triglyceride molecule can be shown as illustrated below, where each of the R1, R2, and R3 groups represents a hydrocarbon chain portion which is the residue of some particular fatty acid molecule:

If all three of the fatty acids are identical, the triglyceride can be called a “simple” triglyceride; by contrast, if two or three different types of fatty acid residues are present, the triglyceride can be called a “mixed” triglyceride.
Triglyceride formation is a very important natural metabolic process in both plants and animals. In animals, triglycerides are the fundamental molecular building blocks of fat; as an animal accumulates fat, it does so by coupling fatty acid molecules to glycerol molecules, mainly forming triglycerides, with relatively small quantities of diglycerides and monoglycerides usually also present. The result is a chemical form of energy storage, which is very valuable in evolutionary terms, because the animal can conveniently store triglycerides (in fatty tissue) when food is plentiful, and can later break down its stored triglycerides, using that process to generate energy if food becomes scarce.
Only a relatively few plants form triglycerides in substantial quantities. However, because of the dietary and commercial usefulness of vegetable oils, a number of plants that synthesize and accumulate triglycerides (usually in the grain, nut, fruit, or other edible portion) have been identified and turned into crop plants. These crop species have been selectively bred (some for thousands of years) by farmers, plant scientists, and others, to create crop strains that generate relatively large quantities of triglycerides. Commercially important vegetable oils from these plants include corn oil, olive oil, safflower oil, peanut oil, palm oil, rapeseed oil, soybean oil, cottonseed oil, coconut oil, canola oil, etc. In general, it is conventional to refer to triglycerides extracted from plant sources as oils, rather than as fats.
The largest commercial sources of animal fat include beef fat (which includes beef tallow), pork fat (which includes pork lard), poultry fat (which can include chicken and/or turkey fat), and fish oils.
The particular types of fatty acid molecules created by different species of animals and plants vary substantially, in terms of molecular size. Most species of plants and animals that are of commercial interest create fatty acids with at least about 10 carbon atoms, up to about 25 carbon atoms and sometimes higher, in the “fatty” portion of the chain. Most fatty acids that are common in nature tend to have between 10 and 20 carbons; examples include lauric acid (10 carbons), palmitic acid (16 carbons), and stearic acid (18 carbons), all of which are saturated, as well as oleic, linoleic, and linolenic acid (all with 18 carbons, and with 1, 2, and 3 unsaturated bonds, respectively), and arachidonic acid (20 carbons, 4 unsaturated bonds).
At the very short end of the fatty acid range, fatty acids with fewer than about 10 carbon atoms tend to be thin (i.e, watery and non-viscous) and volatile, and are not as easy to handle or as commercially valuable as compounds that form oils which are stable and will not evaporate rapidly at normal room or handling temperatures. At the long end of the spectrum, fatty acids with more than about 25 carbon atoms tend to be heavier and thicker, and are often solid at room temperature; accordingly, they are present in beef tallow, pork lard, and other forms of fat that are solid at room temperature. They typically can be converted into liquified form merely by heating them to cooking temperatures.
Another important variation in the molecular structures of fatty acids synthesized by different animal and plant species involves unsaturated bonds. These occur when two adjacent carbon atoms, in a chain, are bonded to each other by a double-bond. Different species of plants and animals create varying different mixtures, ratios, and concentrations of unsaturated bond numbers and placements, in the complex mixture of fatty acids that an animal or plant synthesizes naturally.
For purposes of discussion herein, it is presumed that: (i) any higher animal or plant will synthesize a mixture of various different fatty acids; (ii) substantial variations will be present in the triglyceride mixture that is present in any single animal or plant; and, (iii) even larger variations will be present in the triglyceride mixture contained in a large batch of vegetable oil or animal fat that was prepared from numerous different plants or animals. These variations (in chain length, and in numbers and placements of unsaturated bonds) will show up in subtle differences in the carbon chains that are represented by the R1, R2, and R3 groups in a triglyceride, as illustrated above. Fortunately, these types of subtle differences in the fatty acid chains of triglyceride compounds do not impede the chemical treatment of such oil or fat preparations, using the methods disclosed herein, to create flavor/palatability enhancers for pet foods.
It is also presumed that in any large batch of vegetable oil or animal fat prepared from numerous plants or animals, substantial quantities of monoglycerides and diglycerides are also likely to be present. Fortunately, these compounds also do not interfere with the chemical treatment of oil or fat preparations using the methods disclosed herein, to create flavor/palatability enhancers for pet foods. Accordingly, when a vegetable oil or animal fat preparation is referred to herein as a triglyceride-containing preparation (or mixture, or similar substance), this is not meant to imply or suggest that the preparation, mixture, or substance contains only triglycerides. Instead, it merely indicates that the preparation, mixture, or substance contains large numbers of triglyceride molecules, in addition to any monoglycerides, diglycerides, lipids, proteins, carbohydrates, water, or other molecules that may be present. As used herein, the term “triglyceride” is simply a chemical term which includes the dominant components of both vegetable oil, and animal fat.
It also should be recognized that several types of chemical processing of oils and fats are well-known and widely used. One example is “saponification”, which comes from the same root word as “soap”. This term refers to treatment of a fat using a strong alkaline agent, such as caustic soda (also known as alkali, lye, sodium hydroxide, or NaOH). This treatment breaks apart the ester bonds that were formed when fatty acids became bonded to glycerol. This releases and/or regenerates the fatty acids (or modified versions thereof, such as their sodium salts).
Another important form of processing fats is called hydrogenation; in this process, a hydrogen-donating compound is used to convert the double bond(s) in an unsaturated carbon chain into single bonds, thereby creating a fully saturated carbon chain.
Still another well-known method of processing fats is called “rendering”, which refers to cooking a fatty compound, usually by boiling the fatty compound with water present. This causes hydrolytic breakage of the ester bonds and/or carbon chains, in a manner which releases the fatty acids and/or smaller hydrocarbons.
Another type of processing involves enzymes, such as “lipase” enzymes, which typically cleave off fatty acids. Yet another form of processing uses metallic or crystalline compounds as catalysts; this is similar to the type of “catalytic cracking” that is used to break asphalt and heavy crude oils into smaller hydrocarbons that are valuable as gasoline, kerosene, or other fuels or lubricants.
Still another chemical name, “pyrolysis”, has been given to the chemical reactions that occur when fat is heated to a sufficiently high temperature to cause it to brown, sear, etc. Pyrolysis occurs when an oily or fatty compound is fried or grilled, such as in a restaurant, or in a large-scale manufacturing facility which prepares certain types of cooked foods.
These forms of processing are of interest herein, because nearly all of them leave behind residues, including (in many cases) fatty residues which have foul and disgusting odors, and which must be disposed of as noxious and potentially toxic wastes. The methods of this invention may be useful for treating any particular such residue, to convert it into a valuable product; this can be evaluated on a case-by-case basis, using the unwanted residue from any such known process that is used to commercially treat any fatty or oily preparation.
Accordingly, one object of this invention is to disclose a new class of flavor/palatability enhancers, for foods that are manufactured and marketed for companion animals such as dogs or cats, which can be made by using vegetable oil and/or animal fat as a major starting ingredient.
Another object of the subject invention is to provide a new type of flavor enhancer, for use as a low-volume coating on pelleted or extruded kibbles or molded biscuits, for pets.
Another object of this invention is to disclose a new class of flavor/palatability enhancers, which can be coated onto the surfaces of dry or semi-dry foods for pets.
Another object of this invention is to disclose a method of chemically treating the residues that are created by treating fatty or oily compounds using a process such as saponification, rendering, enzymatic digestion, catalytic refining, etc., to render those residues commercially useful and valuable.
These and other objects of the invention will become more apparent through the following summary, drawings, and description of the preferred embodiments.